1. Field of the Invention
The present general inventive concept relates to a hard disk drive, and more particularly, to an actuator arm having an arm hole with an optimized shape to improve dynamic characteristics, and an actuator assembly having the same.
2. Description of the Related Art
A hard disk drive (HDD) is an information storage device of a computer that stores and reproduces data on a disc using a read/write head. The hard disk drive uses an actuator to move the read/write head to the desired position to read/write data.
FIG. 1 is a plan view illustrating an actuator assembly 10 of a conventional hard disk drive.
Referring to FIG. 1, the actuator assembly 10 of the hard disk drive moves a read/write head 16 for recording and reproducing data to and from a certain position above a data storage disk (not shown). The actuator assembly 10 includes an actuator arm 12 rotatably coupled to a pivot shaft 11 installed on a base member (not shown) of the hard disk drive. The actuator arm 12 includes, at its leading end, a suspension 14 for supporting a slider 15 biasing the head 16 against the surface of the disk, and at its middle portion, a substantially triangular arm hole 13 for reducing a weight of the arm 12. A voice coil 17 is coupled to the rear end of the actuator arm 12. A magnet 18 is arranged opposite the voice coil 17. The voice coil 17 and the magnet 18 form a voice coil motor (VCM) for rotating the actuator arm 12.
The voice coil motor is controlled by a servo control system so that the actuator arm 12 is rotated according to Fleming's left-hand rule by an interaction between an input electric current of the voice coil 17 and a magnetic field of the magnet 18. When the hard disk drive is turned on and the disk starts to rotate, the VCM moves the actuator arm 12 to move the read/write head 16 to a position above a data recording surface of the disk. From there, the read/write head 16 traces a track on the data recording surface of the disk to record or reproduce data. When the hard disk drive is turned off and the disk stops rotating, the VCM moves the actuator arm 12 in an opposite direction to move the read/write head 16 away from the data recording surface of the disk.
Recently, tracks of the disk have become narrower as the recording density increases, so that it is necessary to increase precision for position control of the read/write head. A major resonance mode of the actuator arm has an effect on the precision of the position control of the read/write head. The major resonance mode of the actuator arm means a vibration mode of bending deformation of the actuator arm, and is also referred to as a butterfly mode. The major resonance mode of the actuator arm is caused by an operation of an actuator assembly. When a force is input to a voice coil to operate the actuator assembly, as an output, the read/write head is displaced. As displacement of the read/write head increases, a position error signal (PES) increases, deteriorating reliability of reproducing and recording data. Accordingly, in order to reduce the PES, it is necessary to minimize the displacement of the read/write head.
FIG. 2 illustrates an actuator assembly as disclosed in Japanese Patent Laid-Open No. 2003-141826.
Referring to FIG. 2, an actuator arm 21 has an arm hole 23 which gives the actuator arm 21 a bar linkage structure. That is, the actuator arm 21 has a shape defined by a leading portion 25, a rear portion 24, and a middle portion 26. When the leading portion 25, the rear portion 24, and the middle portion 26 define a shape of the arm hole 23, widths of the leading portion 25 and the rear portions are narrower than that of the middle portion 26. The lesser widths of the rear and leading portions 24 and 25 of the actuator arm 21 create a hinge of the bar linkage structure.
FIG. 3 shows displacement MX of a read/write head in a major resonance mode of a conventional actuator arm with a bar linkage structure.
Referring to FIG. 3, it can be understood that since the actuator arm has the bar linkage structure, the displacement of the read/write head in the major resonance mode can be minimized.
However, referring to FIG. 7 and Table 1 to be described later, the actuator arm has a drawback in decreasing a frequency of the major resonance mode although the actuator arm with the bar linkage structure has the advantage of increasing the gain margin. This is undesirable, even when the actuator arm require a narrow bandwidth for position control of the read/write head.